Bridging the Brahmaputra: India’s longest rail-cum-road bridge inaugurated in Assam

India’s longest rail-cum-road bridge inaugurated in Assam

With the commissioning of the 4.94 km Bogibeel bridge in Assam, India completed its longest rail-cum-road bridge, which is also Asia’s second longest rail-road link. In a much-awaited move, the central government inaugurated the bridge on December 25, 2018, providing connectivity between Assam and Arunachal Pradesh besides playing a crucial role in defence movement along the India-China border in Arunachal Pradesh. The engineering masterpiece boasts of several unique features such as its fully welded structure and corrosion-resistant steel plates. While there were many geographic and administrative hurdles and a delay of 16 years from its conception, the completion of the Bogibeel bridge has certainly set a new benchmark for bridge construction in the country.

Journey so far

The Bogibeel bridge, situated 17 km downstream of Dibrugarh and Dhemaji, is the sixth rail-road bridge on the Brahmaputra river in Assam. The project was approved by the Cabinet Committee on Economic Affairs in September 1997 and Northeast Frontier Railway (NEFR) was entrusted with its implementation. The pre-construction studies, geotechnical investigations and detailed design study of the rail-road bridge were undertaken by RITES Limited. The foundation stone for the project was laid on April 22, 2002. However, construction work only picked up pace after it acquired national project status in 2007.

In April 2008, the contract for the construction of the foundations and substructure of the bridge was awarded to Gammon India. Bhartia Infra Projects Limited was entrusted with the construction of guide bunds and approach embankments on the south bank of the bridge. In November 2011, Hindustan Construction Company [HCC] Limited, in a joint venture with DSD Brouckenbau GmbH, Germany, and VNR Infrastructures Limited, secured an order worth Rs 9.87 billion for construction of the superstructure of the bridge. While HCC held a majority share of 51 per cent, VNR Infrastructures Limited and DSD Brouckenbau GmbH had a share of 29 per cent and 20 per cent respectively.

In April 2014, SGS, a leading inspection, verification, testing and certification company, was commissioned by the NEFR to provide third-party technical inspection for the project. Over the course of the next four and a half years, a team of 21 SGS experts was deployed on site to conduct a wide range of technical inspections, including welding testing and non-destructive testing. “Our independent technical inspection services helped to build this heavy-duty structure, which is designed to bear heavy weights and heavy moving loads, and ensure compliance with the relevant quality standards to be best in class,” says Cresenciano G. Maramot, managing director, SGS India.

In October 2015, the cost of the bridge project escalated by Rs 3 billion on account of a change in the bridge design. As per the earlier design, only 36 girders had to be constructed for the superstructure. This was, however, increased to 41. After a trial run in October 2018, the bridge was finally commissioned on December 25, 2018.

Distinguishing features

“The Bogibeel bridge has many technical firsts to its name. It is India’s first fully welded Warren truss girder-type steel bridge,” says Arjun Dhawan, director and group chief executive officer, HCC Limited. “Not only has an incremental launching technique for superstructure erection been used for the first time in India, it is also the world’s longest incrementally launched steel bridge,” he adds. It is also for the first time that European codes and welding standards were adhered to in the construction of a bridge in India.

The main bridge foundation has 42 double D-shaped wells, each with a steining thickness of 3 metres and diaphragm thickness of 2.5 metres. The foundation of the bridge is 58.6 metres deep except for the abutment and shore well where depths are 42 metres and 68.75 metres respectively. The substructure of the bridge consists of twin circular hollow piers with an outer diameter of 5.3 metres and inner diameter of 3.3 metres. The superstructure of the Bogibeel bridge is a double-decked composite-welded Warren truss with two railway tracks on the lower deck and a three-lane road on the upper deck, flanked by footpaths on each side. The trusses make the connection between different components of the bridge a permanent one, thereby eliminating the need for periodic replacement as is the case with bolts and rivets. Therefore, it not only reduces the maintenance cost but also enhances the longevity of the superstructure. The Bogibeel bridge is estimated to be serviceable for a span of about 120 years.

In order to reduce corrosion, the superstructure of the bridge has been constructed using special copper-bearing steel plates. Given the excessive humidity in the region, a complex corrosion protection system specific to different components of the bridge has been deployed. Besides, seismic restrainers have been provided to offer greater stability to the heavy spans.

Making of the bridge

HCC Limited deployed “Most 2D” automatic nesting software to generate efficient two-dimensional cutting plans for fabricating the steel superstructure of the bridge. The nesting technology was based on advanced cutting algorithms specifically designed to optimise the cutting layouts in shearing.

For bridge construction, HCC set up facilities on the left bank of the Brahmaputra that had three sequences of fabrication, assembly and launching. The fabrication shops, with a capacity of 2,000 million tonnes (mt) per month, assembled customised platforms in-house to fabricate and fit various joints by using gas metal arc welding. Further, tests such as magnetic particle testing, dry penetration testing and ultrasonic testing were used to ensure error-free welding. For the first time in the country, a specialised beam-making coordinate measuring machine from Italy was used for fabrication of box and I-sections. After the fabrication process, the sections were installed on their designated beds in the assembly shop. Hydraulic jacks and strand jacks with a capacity of 1,000 tonnes were linked with the substructures to move the steel truss over the pillars. This eliminated the need of entering the turbulent river and also accelerated the pace of project execution.

For the Bogibeel project, a combination of rail and road transport was used to deliver 80,000 tonnes of steel plates from various parts of the country to the project site. Of this, around 25 per cent of the steel was categorised as over-dimension cargo and, therefore, required special measures for transportation to the site. The steel plates and sections were procured mainly from three firms – Jindal Steel and Power Limited, Essar Steel, and Steel Authority of India Limited. The average lead time for procuring these materials was four months. The spherical bearings used for the bridge were inspected in Germany, shipped to China for load testing and then to Bhopal for refitting of tested bearings and finally to the project site. The lead time of such consignments was six months.

Around 3 million cement bags went into the making of the bridge. The average daily consumption of welding wire was about 2,000 kg and that of grinding wheels around 5,000. Besides 450,000 shear studs were imported from the US, around 700,000 high-strength friction grip bolts were manufactured at different sources in India and metal polymer Diamant MM1018FL gap compensation was imported from Germany.

Challenges on the way

The construction of the bridge was impeded by several challenges. One of the stiffest challenges was the construction of the guide bunds on the turbulent Brahmaputra in short spells of four to five months a year as intense rainfall and frequent floods restricted the construction work period. This demanded huge mobilisation of equipment required for project execution. Another major challenge faced was the transportation of concrete across river channels of 600-900 metre width from both banks. This was overcome by pumping the concrete through a pipeline laid over buoys with multiple concrete pumps. Further, finding the required skilled manpower and convincing them to work in the hostile climate conditions also posed a challenge for the project. The inordinate delay resulting from these issues caused an escalation of 74 per cent in the project cost from the original estimate of Rs 32.3 billion to Rs 56.2 billion.

Benefits galore

The newly constructed bridge will provide connectivity between the Rangia-Murkongselek section of the NEFR on the north bank and the Lumding-Dibrugarh section that lies to the south of the Brahmaputra river. A new railway station in Dibrugarh, expected to be the largest in the region, has been proposed and is to be linked to the Rangia-Murkongselek line via Chaulkhowa and Moranhat. Indian Railways has initiated the gauge conversion of the Dhamalgaon-Sisiborgaon rail line to the north of the Bogibeel bridge and has commissioned the 44 km Chaulkhowa-Moranhat line to the south.

The bridge will also provide a major impetus to the defence forces as it will provide rapid connectivity to areas near the India-China border. This would mean faster evacuation of troops and heavy weapon systems.

The bridge will reduce travel time from Assam to Arunachal Pradesh to four hours. It will also reduce travel time by train from Delhi to Dibrugarh by about three hours to 34 hours as against 37 hours at present. Meanwhile, tourist places in Arunachal Pradesh will become more accessible and provide  a fillip to the tourism industry. The bridge will also cut down the distance to the border with China by 10 hours.

By connecting two crucial highways of Assam – National Highway (NH)-37 and NH-52 – the bridge will enhance the intra-state and interstate trade ecosystem. At present, any cargo generated on either side of the national highways takes at least 10 to 12 hours to reach its destination. The Bogibeel rail-road link will significantly reduce this transshipment time to a maximum of two hours, thus saving the unnecessary extra cost of transportation and time too.

Setting high standards

In recent years, road and bridge construction and rehabilitation works have picked up pace with the central government assigning top priority to enhancing road connectivity to the Northeast. The major projects undertaken in the region include the Saraighat bridge II and the Dhola-Sadiya bridge. The inauguration of the Bogibeel bridge has set an example for the successful execution of projects of similar scope and size and faced with similar challenges. The expertise gained from the construction of this bridge can be utilised in other upcoming and ongoing projects. The government has already set forth plans to construct a 19.3 km bridge over the Brahmaputra river connecting Dhubri in Assam to Phulbari in Meghalaya. However, issues such as delays in land acquisition and pre-construction activities, geological surprises, lack of competence in handling critical and complex construction, limited availability of skilled manpower, and safety issues need to be dealt with to ensure smoother project execution.

Deeksha Soni with Liya Rashid